Fan system and method for controlling a fan motor

ABSTRACT

In a fan system for an internal combustion engine of a motor vehicle, having an electrical fan motor with a commutator, and having a control unit which detects a fault in the fan motor and switches said motor to a voltage-free state if the motor current reaches a predetermined load-dependent switch-off value, the invention proposes that the control unit controls the fan motor with at least a virtually maximum power for a predetermined period of time if the motor current reaches a load-dependent switching value which is lower than the associated switch-off value by a predetermined amount. As a result, the fan motor is not switched off in an undesirable manner if only contamination, but not blocking, is present.

BACKGROUND OF THE INVENTION

The invention relates to a fan system for carrying out controlledcooling for an internal combustion engine of a motor vehicle, having anelectrical fan motor which has a commutator, and having a control unitfor controlling the fan motor, the control unit being configured in sucha manner that it detects a fault in the fan motor, in particular a powerconsumption which is increased in comparison with the stipulation, andswitches said motor to a voltage-free state if the motor current reachesa predetermined load-dependent switch-off value. The invention alsorelates to a method for controlling a fan motor.

A fan system of the generic type with blocking detection via thecurrent/voltage characteristic curve is known, for example, from DE 10326 785 A1.

Cooling systems for modern motor vehicle drives are provided withpowerful fan motors which drive a fan wheel or cause the latter torotate in order to be able to provide the heat exchangers of the coolingsystem with a sufficiently high air mass flow even at a standstill, thatis to say when the motor vehicle is stationary, or in the case of onlylow vehicle speeds. The fan motors usually used are DC motors whoserotor provided with coils is supplied with electrical energy via acommutator with a brush arrangement. According to the prior art, suchfan motors are controlled using a relay circuit, which has up to threeseries resistors and implements different loads or rotational speeds ofthe fan, or using power electronics which generate periodicpulse-width-modulated control signals, the duty ratio of which can bevaried, for the purpose of virtually infinitely variable control.Although fan motors generally have to be designed for a high maximumrequired cooling power, the motors are loaded only with a considerablylower power and thus with a lower current for a large part of the totaloperating time during normal operation.

Faults may occur during operation of the fan motor, which faults cause,in particular, blocking or sluggishness of the fan motor. Since furtherenergization of the DC motor in such a situation may result in thecontrol electronics and the fan motor being damaged as a result ofoverheating, an attempt is usually made to detect blocking of the DCmotor in good time in order to interrupt the flow of current through theDC motor if blocking is detected. In modern fan systems, the requiredrotational speed monitoring is not carried out with the aid of arelatively complicated rotational speed sensor, but rather an attempt ismade to detect the rotational speed only on the basis of evaluation of apower consumption of the DC motor. It is assumed that the blocked DCmotor has a considerably higher power consumption than would be the casewhen a motor under load is operating correctly. However, thecurrent/voltage characteristic curve of the fan motor is dependent onfurther factors, for example the temperature of the fan motor, itssupply voltage, manufacturing tolerances and the vehicle speed. Onaccount of such influences and inaccurate detection of the current, thepower consumption of the DC motor may vary by a factor of greater thanone, generally at least a factor of two in the case of powerful DCmotors, in the same operating state.

However, problems arise with the known detection of fan system blockingif the motor current is increased, for example on account of wear, inparticular pasting of the commutator, and thus results in unwantedswitching-off of the fan motor by the control device. Such “pasting”, inwhich coal dust, dirt, oil and so on settles in the slots between thecontact laminations of the commutator, the pasting often beingconductive as a result of the coal dust and/or the commutator abrasionand thus causing a short circuit between the laminations, regularlyoccurs on account of the fan motor being permanently controlled with anexcessively low current or an excessively low rotational speed.

In the case of a fan system without blocking detection, known from DE 102005 016 452 A1, it is known practice to control the fan motor with agreatly increased power at a predetermined time, that is to sayirrespective of the actual power consumption, in order to avoid orreduce pasting so that the pasting is either expelled from the fan motoror is burnt away.

SUMMARY OF THE INVENTION

In a fan system whose power consumption is monitored in order to detectfaults, the object of the invention is therefore to avoid or reduceunwanted switching-off of the fan motor, in particular on account ofpasting of the commutator.

In the fan system according to the invention, the control unit isconfigured in such a manner that it controls the fan motor with at leasta virtually maximum power for a predetermined period of time if themotor current reaches a load-dependent switching value which is lowerthan the associated switch-off value by a predetermined amount.

The fan system of the present invention has the advantage that, whenpasting begins or becomes greater, as a result of which its powerconsumption approaches the switch-off threshold, the fan motor isswitched on, thus cleaning the fan motor and preventing undesirableswitch-off, since, on account of the cleaning, the power consumption ismoved away from the switch-off threshold if only pasting and notblocking was present. It is also advantageous, in particular, that thefan motor is not switched on independently of the requirements atarbitrary times but rather if more or less great actual pasting ispresent according to the power consumption.

According to a first development of the invention, the switching valuesare each approximately 10% lower than the associated switch-off values,which provides advantages, in particular, with respect to a resolutionwhich is not too complex when detecting the current. In particular,there is no need for any additional outlay on hardware.

According to one advantageous development of the invention, thepredetermined period of time is less than 60 seconds, preferablyapproximately 10 seconds. On the one hand, this generally suffices toclean the commutator slots and, on the other hand, the load on the fanmotor, whose power consumption is increased in comparison with normalfull load on account of the pasting, is kept low.

In another development of the invention which is considered to beparticularly advantageous, the switch-off values and/or the switchingvalues are each stored in the form of a characteristic curve in thecontrol unit. This makes it possible for the required information to beacquired and used in a simpler and more precise manner than proposed,for example, in the generic prior art mentioned at the outset.

Another aspect of the present invention provides a method forcontrolling a fan motor for an internal combustion engine of a motorvehicle. In this case, an item of information relating to the currentthrough the fan motor is determined, and a fault in the fan motor isdetected and the fan motor is switched off if the motor current reachesa predetermined load-dependent switch-off value. Furthermore, the fanmotor is controlled with at least a virtually maximum power for apredetermined period of time if the motor current reaches aload-dependent switching value which is lower than the associatedswitch-off value by a predetermined amount.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail below using exemplaryembodiments. In the drawing:

FIG. 1 shows a schematic block diagram of a fan system according to theinvention for an internal combustion engine,

FIG. 2 shows a schematic illustration of a commutator of the fan motor,and

FIG. 3 shows a current characteristic curve diagram for an exemplary fanmotor.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a block diagram of a fan system 1 foran internal combustion engine (not shown) in a motor vehicle. The fansystem 1 has a blower with a fan motor 2. The fan motor 2 iselectrically connected to a control unit 3 which controls the fan motor2 in an infinitely variable manner according to the blower requirementof the motor management system and further acquired information, inparticular the temperature and the supply voltage U_bat of the fan, in asuitable manner with a manipulated variable, usually a voltage. The fanmotor 2 has a commutator (not illustrated here).

Such a commutator 4 is schematically illustrated in FIG. 2. Thecommutator 4 to which, for example, eight contact laminations 5 arefitted is seen, which contact laminations are arranged in anelectrically insulated manner on a shaft 6 of the fan motor 2. Thecontact laminations 5 are electrically connected to rotor coils of thefan motor 2. Slots which electrically insulate the contact laminations 5with respect to one another are situated between the contact laminations5. Contact is made with the laminations 5 with the aid of so-calledbrushes 7 which are pressed onto the laminations 5 with a spring force,with the result that there is continuous contact. An electrical currentpasses to the rotor coils of the fan motor 2 via the brushes 7. Duringoperation of the motor, the brushes 7 slide on the laminations 5 andcause, for example, abrasion which preferably settles as dust in theslots between the laminations 5. Since other materials in the immediatesurroundings also settle in the slots, a “paste” which is substantiallyconductive forms. The fan motor 2 is shown, by way of example, for atwo-pole motor with two carbon brushes. Four-pole motors with two orfour brushes or six-pole motors with two or four or six brushes are alsopossible.

A characteristic curve of the motor current I_motor, which depicts thefan current requirement dependent on the blower requirement during“normal operation”, is illustrated in the lower region of the currentcharacteristic curve diagram according to FIG. 3. All of thecharacteristic curves in FIG. 3 apply, by way of example, to a constanttemperature or other factors which are kept constant. A currentswitch-off characteristic curve I_switch-off which can be seen in theupper region of FIG. 3 is stored in the control unit 3 as a function ofthe motor voltage, supply voltage, temperature, time etc. If theswitch-off value dependent on the respective blower requirement (motorvoltage) is reached on the characteristic curve I_switch-off, the fanmotor 2 is switched to a voltage-free state. Since these switch-offvalues would also be reached, without a fault or blocking, when onlymore or less great pasting of the commutator 4 is present, the fan motor2 would be switched off in an unwanted manner by the control unit 3 inthese cases. In order to avoid this, a second switching characteristiccurve I_switch_2 is stored in the control unit 3, again as a function ofthe motor voltage, supply voltage, temperature, time etc. However, therespective switching value on the characteristic curve I_switch_2 islower than the associated value in the switch-off characteristic curveI_switch-off. A value which is lower by approximately 10%, for example,is useful, in particular with regard to a resolution which can beachieved with acceptable outlay when detecting the current. When thisswitching characteristic curve I_switch_2 is reached, the DC motor 2 isfully controlled for a time to be stipulated, for example 10 seconds, ifthere is a blower requirement from the motor management system. As aresult of this full control, particles in the commutator slots areremoved and operation of the fan motor which is still fault-free isensured.

The fan motor 2 may also be switched on for a longer period of time ifthe motor and the control device are designed for a correspondinglylasting increased power consumption. While switching on the fan motor 2,the upper limit I_switch-off continues to remain in force and is notreached if only pasting and not blocking is present.

1. A fan system for carrying out controlled cooling for an internalcombustion engine of a motor vehicle, having an electrical fan motorwhich has a commutator, and having a control unit for controlling thefan motor, the control unit being configured in such a manner that itdetects a fault in the fan motor and switches said motor to avoltage-free state if the motor current reaches a predeterminedload-dependent switch-off value, characterized in that the control unitcontrols the fan motor with at least a virtually maximum power for apredetermined period of time if the motor current reaches aload-dependent switching value which is lower than the associatedswitch-off value by a predetermined amount.
 2. The fan system accordingto claim 1, characterized in that the switching values are each 5 to 20%lower than the associated switch-off values.
 3. The fan system accordingto claim 2, characterized in that the switching values are eachapproximately 10% lower than the associated switch-off values.
 4. Thefan system according to claim 1, characterized in that the predeterminedperiod of time is less than 60 seconds, preferably approximately 10seconds.
 5. The fan system according to claim 1, characterized in thatthe switch-off values and/or the switching values are each stored in theform of a characteristic curve in the control unit.
 6. A method forcontrolling a DC fan motor for an internal combustion engine of a motorvehicle, an item of information relating to the current through the fanmotor being determined, and a fault in the fan motor being detected andthe fan motor being switched off if the motor current reaches apredetermined load-dependent switch-off value, characterized in that thefan motor is controlled with at least a virtually maximum power for apredetermined period of time if the motor current reaches aload-dependent switching value which is lower than the associatedswitch-off value by a predetermined amount.
 7. The method according toclaim 6, characterized in that the switching values are each selected tobe 5 to 20%, in particular approximately 10%, lower than the associatedswitch-off values.